Polymers produced with a multimodal molecular weight distribution offer unique product properties. Multimodal products, particularly bimodal products, can be produced by various methods, such as mixing different polymers, producing multimodal polymers under a series of reaction conditions, and reacting different catalysts under a single reactor condition. One method that has proven to be commercially viable, is the production of multimodal catalyst systems wherein a catalyst system comprises more than one catalyst or catalyst component, thus, in effect, providing more than one active site to polymerize monomers during the polymerization process. When fed to a reaction system, each catalyst component concurrently produces a polymer component with distinct product properties. The net result is a polymer composition with distinct product advantages.
U.S. Pat. Nos. 6,605,675, 6,846,886, 6,956,089, 6,689,847, 6,274,684, 6,841,631, 6,894,128, 6,534,604, and PCT publications WO 2002/046243 and WO 2001/030861, generally, describe processes and techniques for making multimodal catalyst systems, and polymerizing with these multimodal catalyst systems. For example, these references discuss bimodal catalyst compositions comprising a combination of a Group 15 containing metal compound (a bisamide compound) and a metallocene compound. One of the advantages of these multimodal catalyst systems lies in the molecular weight split (ratio of high to low molecular weight polymer produced). However, the catalyst system productivity and molecular weight split of polymer produced with these multimodal catalysts can be significantly affected by degradation due to aging of the multimodal catalyst.
“Aging” is typically described as catalyst deactivation or loss of catalyst system productivity, over time. This problem is exacerbated when the catalyst systems includes two or more catalyst components that age at different rates. The degree of aging is typically ascertained by measuring the activity or productivity of a given catalyst batch over an extended period. Because the catalyst system can change over a period of time such as days or months, either in whole or in part by its respective catalyst components, exploring this phenomenon usually requires time and significant resources. Furthermore, multiple samples and polymerization tests are required to assure meaningful results.
Various methods and systems for testing catalyst systems have been developed. For instance, Brummer, Oliver et al., “High-Throughput Screening Applied To Process Development,” Handbook of Combinatorial Chemistry, Vol. 2, 2002, pages 864-884, Boussie, T. R. et al., “A Fully Integrated High-Throughput Screening Methodology for the Discovery of New Polyolefin Catalysts: Discovery of a New Class of High Temperature Single-Site Group (IV) Copolymerization Catalysts,” Journal of the American Chemical Society (2003), 125(14), pages 4306-4317, Murphy, Vince et al., “High-Throughput Approaches For The Discovery And Optimization Of New Olefin Polymerization Catalysts,” Chemical Record (2002), 2(4), pages 278-289, and Boussie T. R. et al., “A Fully Integrated High-Throughput Screening Methodology For The Discovery Of New Polyolefin Catalysts: Discovery Of A New Class Of High Temperature Single-Site Group (IV) Copolymerization Catalysts,” Journal of the American Chemical Society (2003), 125(14), pages 4306-17, generally, discuss methods of using high-throughput screening methods and devices in the development and evaluation of catalyst systems. Various test methods are also discussed in U.S. Pat. No. 6,440,745, U.S. Patent Application Publication No. 2003/161763, and PCT publications WO 1999/064160, WO 2001/098371, and WO 2000/009255.
Other background references include WO 2005/068076, WO 2006/022918, and WO 2006/086104.
Accordingly, there exists a need to understand the effects of aging and catalyst systems such as multimodal catalyst systems, and in turn, to control their aging. There is a further need to polymerize olefins with these catalyst systems to produce, for example, multimodal polymer compositions while being able to predict and control certain process and product properties, such as, for example, catalyst system productivity and polymer properties such as, for example, molecular weight distribution.